Transcript Document

The Peripheral Nervous System
(PNS)
Part A
Peripheral Nervous System
(PNS)
• PNS – all neural structures outside the
brain and spinal cord
• Includes sensory receptors, peripheral
nerves, associated ganglia, and motor
endings
• Provides links to and from the external
environment
Sensory Receptors
• Structures specialized to respond to
stimuli
• Activation of sensory receptors results in
depolarizations that trigger impulses to the
CNS
• The realization of these stimuli, sensation
and perception, occur in the brain
Receptor Classification by Stimulus
Type
• Mechanoreceptors – respond to touch, pressure,
vibration, stretch, and itch
• Thermoreceptors – sensitive to changes in
temperature
• Photoreceptors – respond to light energy (e.g.,
retina)
• Chemoreceptors – respond to chemicals (e.g.,
smell, taste, changes in blood chemistry)
• Nociceptors – sensitive to pain-causing stimuli
Receptor Class by Location:
Exteroceptors
• Respond to stimuli arising outside the
body
• Found near the body surface
• Sensitive to touch, pressure, pain, and
temperature
• Include the special sense organs
Receptor Class by Location:
Interoceptors
• Respond to stimuli arising within the body
• Found in internal viscera and blood
vessels
• Sensitive to chemical changes, stretch,
and temperature changes
Simple Receptors: Unencapsulated
Table 13.1.1
Simple Receptors: Encapsulated
Table 13.1.2
Simple Receptors: Encapsulated
Table 13.1.3
Simple Receptors: Encapsulated
Table 13.1.4
Structure of a Nerve
• Nerve – cordlike organ of the PNS
consisting of peripheral axons enclosed by
connective tissue
• Connective tissue coverings include:
– Endoneurium – loose connective tissue that
surrounds axons
– Perineurium – coarse connective tissue that
bundles fibers into fascicles
– Epineurium – tough fibrous sheath around a
nerve
Structure of a Nerve
Figure 13.3b
Classification of Nerves
• Sensory and motor divisions
• Sensory (afferent) – carry impulse to the
CNS
• Motor (efferent) – carry impulses from
CNS
• Mixed – sensory and motor fibers carry
impulses to and from CNS; most common
type of nerve
Peripheral Nerves
• Mixed nerves – carry somatic and
autonomic (visceral) impulses
• The four types of mixed nerves are:
– Somatic afferent and somatic efferent
– Visceral afferent and visceral efferent
• Peripheral nerves originate from the brain
or spinal column
Regeneration of Nerve Fibers
• Damage to nerve tissue is serious
because mature neurons are amitotic
• If the soma of a damaged nerve remains
intact, damage can be repaired
• Regeneration involves coordinated activity
among:
– Macrophages – remove debris
– Schwann cells – form regeneration tube and
secrete growth factors
– Axons – regenerate damaged part
Regeneration of Nerve Fibers
Figure 13.4
Cranial Nerves
• Twelve pairs of cranial nerves arise from
the brain
• They have sensory, motor, or both sensory
and motor functions
• Each nerve is identified by a number (I
through XII) and a name
• Four cranial nerves carry parasympathetic
fibers that serve muscles and glands
Cranial Nerves
Figure 13.5a
Summary of Function of Cranial
Nerves
Figure 13.5b
Cranial Nerve I: Olfactory
• Arises from the olfactory epithelium
• Passes through the cribriform plate of the
ethmoid bone
• Fibers run through the olfactory bulb and
terminate in the primary olfactory cortex
• Functions solely by carrying afferent
impulses for the sense of smell
Cranial Nerve I: Olfactory
Figure I from Table 13.2
Cranial Nerve II: Optic
• Arises from the retina of the eye
• Optic nerves pass through the optic canals
and converge at the optic chiasm
• They continue to the thalamus where they
synapse
• From there, the optic radiation fibers run to
the visual cortex
• Functions solely by carrying afferent
impulses for vision
Cranial Nerve II: Optic
Figure II Table 13.2
Cranial Nerve III: Oculomotor
• Fibers extend from the ventral midbrain,
pass through the superior orbital fissure,
and go to the extrinsic eye muscles
• Functions in raising the eyelid, directing
the eyeball, constricting the iris, and
controlling lens shape
• Parasympathetic cell bodies are in the
ciliary ganglia
Cranial Nerve III: Oculomotor
Figure III from Table 13.2
Cranial Nerve IV: Trochlear
• Fibers emerge from the dorsal midbrain
and enter the orbits via the superior orbital
fissures; innervate the superior oblique
muscle
• Primarily a motor nerve that directs the
eyeball
Cranial Nerve IV: Trochlear
Figure IV from Table 13.2
The Peripheral Nervous System
(PNS)
Part B
Cranial Nerve V: Trigeminal
• Composed of three divisions: ophthalmic
(V1), maxillary (V2), and mandibular (V3)
• Fibers run from the face to the pons via
the superior orbital fissure (V1), the
foramen rotundum (V2), and the foramen
ovale (V3)
• Conveys sensory impulses from various
areas of the face (V1) and (V2), and
supplies motor fibers (V3) for mastication
Cranial Nerve V: Trigeminal
Figure V from Table 13.2
Cranial Nerve VI: Abdcuens
• Fibers leave the inferior pons and enter the
orbit via the superior orbital fissure
• Primarily a motor nerve innervating the
lateral rectus muscle
Figure VI from Table 13.2
Cranial Nerve VII: Facial
• Fibers leave the pons, travel through the
internal acoustic meatus, and emerge
through the stylomastoid foramen to the
lateral aspect of the face
• Mixed nerve with five major branches
• Motor functions include facial expression,
and the transmittal of autonomic impulses
to lacrimal and salivary glands
• Sensory function is taste from the anterior
two-thirds of the tongue
Cranial Nerve VII: Facial
Figure VII from Table 13.2
Cranial Nerve VIII:
Vestibulocochlear
• Fibers arise from the hearing and
equilibrium apparatus of the inner ear,
pass through the internal acoustic meatus,
and enter the brainstem at the ponsmedulla border
• Two divisions – cochlear (hearing) and
vestibular (balance)
• Functions are solely sensory – equilibrium
and hearing
Cranial Nerve VIII:
Vestibulocochlear
Figure VIII from Table 13.2
Cranial Nerve IX:
Glossopharyngeal
• Fibers emerge from the medulla, leave the skull
via the jugular foramen, and run to the throat
• Nerve IX is a mixed nerve with motor and
sensory functions
• Motor – innervates part of the tongue and
pharynx, and provides motor fibers to the parotid
salivary gland
• Sensory – fibers conduct taste and general
sensory impulses from the tongue and pharynx
Cranial Nerve IX:
Glossopharyngeal
Figure IX from Table 13.2
Cranial Nerve X: Vagus
• The only cranial nerve that extends
beyond the head and neck
• Fibers emerge from the medulla via the
jugular foramen
• The vagus is a mixed nerve
• Most motor fibers are parasympathetic
fibers to the heart, lungs, and visceral
organs
• Its sensory function is in taste
Cranial Nerve X: Vagus
Figure X from Table 13.2
Cranial Nerve XI: Accessory
• Formed from a cranial root emerging from
the medulla and a spinal root arising from
the superior region of the spinal cord
• The spinal root passes upward into the
cranium via the foramen magnum
• The accessory nerve leaves the cranium
via the jugular foramen
Cranial Nerve XI: Accessory
• Primarily a motor nerve
– Supplies fibers to the larynx, pharynx, and
soft palate
– Innervates the trapezius and
sternocleidomastoid, which move the head
and neck
Cranial Nerve XI: Accessory
Figure XI from Table 13.2
Cranial Nerve XII: Hypoglossal
• Fibers arise from the medulla and exit the
skull via the hypoglossal canal
• Innervates both extrinsic and intrinsic
muscles of the tongue, which contribute to
swallowing and speech
Cranial Nerve XII: Hypoglossal
Figure XII from Table 13.2
The Peripheral Nervous System
(PNS)
Part C
Spinal Nerves
• Thirty-one pairs of mixed nerves arise
from the spinal cord and supply all parts of
the body except the head
• They are named according to their point of
issue
– 8 cervical (C1-C8)
– 12 thoracic (T1-T12)
– 5 Lumbar (L1-L5)
– 5 Sacral (S1-S5)
– 1 Coccygeal (C0)
Spinal Nerves
Figure 13.6
Spinal Nerves: Roots
Figure 13.7a
Spinal Nerve Innervation: Back, Anterolateral
Thorax, and Abdominal Wall
Figure 13.7b
Cervical Plexus
• The cervical plexus is formed by ventral
rami of
C1-C4
• Most branches are cutaneous nerves of
the neck, ear, back of head, and shoulders
• The most important nerve of this plexus is
the phrenic nerve
• The phrenic nerve is the major motor and
sensory nerve of the diaphragm
Cervical Plexus
Figure 13.8
Brachial Plexus
• Formed by C5-C8 and T1 (C4 and T2 may
also contribute to this plexus)
• It gives rise to the nerves that innervate
the upper limb
Brachial Plexus
• There are four major branches of this
plexus
– Roots – five ventral rami (C5-T1)
– Trunks – upper, middle, and lower, which form
divisions
– Divisions – anterior and posterior serve the
front and back of the limb
– Cords – lateral, medial, and posterior fiber
bundles
Brachial Plexus
Figure 13.9a
Brachial Plexus: Nerves
• Axillary – innervates the deltoid and teres
minor
• Musculocutaneous – sends fibers to the
biceps brachii and brachialis
• Median – branches to most of the flexor
muscles of arm
• Ulnar – supplies the flexor carpi ulnaris
and part of the flexor digitorum profundus
• Radial – innervates essentially all extensor
muscles
Brachial Plexus: Distribution of
Nerves
Figure 13.9c
Brachial Plexus: Nerves
Figure 13.9b
Lumbar Plexus
• Arises from L1-L4 and innervates the thigh,
abdominal wall, and psoas muscle
• The major nerves are the femoral and the
obturator
Lumbar Plexus
Figure 13.10
Sacral Plexus
• Arises from L4-S4 and serves the buttock,
lower limb, pelvic structures, and the
perineum
• The major nerve is the sciatic, the longest
and thickest nerve of the body
• The sciatic is actually composed of two
nerves: the tibial and the common fibular
(peroneal) nerves
Sacral Plexus
Figure 13.11
Dermatomes
• A dermatome is the area of skin
innervated by the cutaneous branches of a
single spinal nerve
• All spinal nerves except C1 participate in
dermatomes
Dermatomes
Figure 13.12